Gabriel, who turned 16 last month, is expected to join Real Madrid in January, with United facing the prospect of losing one of their most highly rated academy prospects before he has made his senior debut.
Giggs, who made 963 appearances for United and won 34 major trophies, believes the youngster would benefit from being patient rather than rushing the next stage of his career.
Speaking on Rio Ferdinand's YouTube channel, the former winger said: "So far in his career everything is going fine, why would you disrupt that? You're on the right track.
"I trained at 15, I didn't play for the first team until two years later so you have to have that patience that people just don't seem to have at the moment."
Giggs made his own first-team breakthrough at 17 and remained a key figure at Old Trafford until retiring at the age of 40. He believes young players can underestimate the demands of senior football, even when they have already impressed at academy level or during pre-season.
"And believe it or not, first-team football for Man United is completely different to playing in the youth team, playing pre-season for the first team, it's completely different.
"That first game, yeah, you might do alright, but you have to do it for 40, 50 games a season. You're going to get injuries, loss of form, bad results, so you have to be patient.
"If you're on the right trajectory then just bide your time, no matter how good you are."
The former Wales international pointed to Arsenal youngster Max Dowman as another example of a teenager who has made an impression without demanding an immediate regular place in the senior side.
"Max Dowman is unbelievable but he's not playing for Arsenal at the moment.
"I'm sure he'll bide his time, I'm sure he's getting impatient, but he's not kicking off, he knows in a couple of years' time he might be the main man for Arsenal."
Gabriel's expected departure is a significant blow for Manchester United, particularly given the excitement surrounding his potential. Giggs' message is that development requires patience, even for players who appear ready to make the step up.
His own career offers a powerful example of the rewards that can come from waiting for the right opportunity, rather than seeking an immediate route into first-team football elsewhere.